3D manipulator stuck on left side of split viewport
It appears that you've hidden the gizmos in the left viewport, which is why the Move gizmo is invisible and the Measure tool gives you an error message. Enable them by clicking the Show Gizmos icon shown below.



Ensure that the following options are enabled in Viewport Gizmos.





The exact error message is "Gizmos hidden in this view" which is printed by view3d_ruler_add_invoke() (view3d_gizmo_ruler.c) when the Measure tool is used and v3d-&gt;gizmo_flag has the V3D_GIZMO_HIDE or V3D_GIZMO_HIDE_TOOL flags set. V3D_GIZMO_HIDE is set when Show Gizmos is disabled and V3D_GIZMO_HIDE_TOOL when Active Tools in the Viewport Gizmos options is deactivated.